Table of Conent

Abstract

The production of local fruits in recent years has been increasing by leaps and bounds that when we consider their annual productivity in 1989 it followed the landing sequence of (in tons) : - durian, 299,346, banana; 200,148, pineapple; 129,144, rambutan; 59,345, cempedak; 80,863, mango; 25,147, duku/langsat; 71,636, watermelon; 81,766, mangosteen; 32,891, ciku; 15,900, jackfruit; 22,504, citrus fruits; 9,558, papaya; 12,423, star-fruit; 7,953 and guava; 54,111 (Table 1A).  In the same context, Table 1B & 1C demonstrate the seasonal fruit conservation in Penang in 1989 together with nonseasonal consumption in 1989 and total production in 1992.  Out of these quite a number of them are exported to Singapore, Hong Kong, Japan and currently venturing into the EC markets where it has to compete   actively with other well established exporters, viz. some African, Caribbean and South American countries.  In this connection, one could consider and  focus initially, in the local context, towards banana, papaya and star-fruit as the prime perishable exportable ones.  This obviously necessitates consideration on aspects of its preservation in order to prolong shelf-life ultimately to achieve a competitive edge in boosting both the local and export requirements.

The most effective means of maintaining perishable commodities fresh and sound is by refrigeration.  However, in recent times, the advantage of refrigeration in retarding biochemical processes have been augmented by systems for reducing oxygen and/increasing Co₂ concentration in the storage or transport environment.  Further, as a consequence in the discovery of plant growth regulators, i.e. ethylene, auxin, cytokinnins, giberellins and inhibitors, substantial amount of indepth  research has been done related to these substances objectively in regulating both ripening and senescence (Leopold and Kriedemann, 1; Looney, 2; McGlasson et al, 3; Wittwer, 4).

Recognition of IAA had also aroused interest in synthetic   growth  regulators leading to the development of numerous auxins, viz. 2,4-dichlorodimethyl hydroxide (diaminozide), synthetic cytokinins, and ethylene-releasing compound 2-choroethylphosphonic acid (ethephon).  Nevertheless, the era of most rapid development of new compounds, new knowledge and new technologies appears to approach a bottleneck.  It is suggestive that a major reason for this is the increased concern in amending foreign chemicals to foods.  In relation, the high costs of development and safety testing of new compounds is no doubt active as a deterrent to the chemical industry.  An additional reason is that basic knowledge of the mode of action of the plant growth regulators and consequently their role in various plant processes is still lacking.  Hence, it is opportune to evaluate and highlight necessities in devising fresh paradigms which will stimulate  new research approaches.

Since ripening is a dramatic even in climacteric fruits, it is widely acknowledged  that ethylene plays a crucial role in the initiation and development of ripening in them while there is less agreement on its function in nonclimacteric fruits.  It is believed that there are two systems in ethylene biogenesis.  System 1 is considered to be responsible for the low level of ethylene present in all fruit tissues, while the second system produces the authocatalytic burst of ethylene production in climacteric fruits such as bananas.  For ethylene to function as an initiator, either the sensitivity of the tissue to the pre-existing endogenous level of ethylene must change/there must be an increase in the endogenous ethylene concentration/both changes must occur.   Nevertheless, the important considerations are not the exact timing of the rise in   ethylene production, but rather what particularly alters the sensitivity of fruit tissues to ethylene, how is the production of ethylene regulated, and what is its function during ripening.

In conjunction attempts have been made to regulate and control the afore-mentioned process incorporating fruit rot by employing naturally occurring yeast/fungi  both in the USA and Israel.  It has been found that variants of a strain of Pichia guilliermondii is effective on a variety of fruits inclusive of peaches, apples, grapes and citrus.  In the Malaysian and Asian context a similar approach  was undertaken with regard to bananas, papayas and star-fruit.

Banana and papaya being both climacteric fruits exhibit a ripening  respiratory pattern involving  the processes of preclimacteric, climacteric rise, climacteric peak and post-climacteric periods in the production of CO₂, uptake of O₂ and culminating in the evolution of C₂H₄ incorporating the involvement of 1-aminocyclopropane- 1-carboxylic acid in ethylene biosynthesis wanting reasonable considerations for its suppression.  Such ripening and browning effects involve phenolic metabolism with special reference to the activity of phenylalanine ammonia-lyase and certain concentrations of chlorogenic acid and catching.   In the export industry of bananas to overcome this process, the harvested bananas are cleaned, treated with fungicide, vacuum packed to be below 300 mg Hg with an O2 content of 0.1%, CO2;  10-15% and ethylene; 0.35 ppm, before storage at a temperature of between 10-14oC having a relative humidity of 85-90%.  At the import destination, when unpacked they are vulnerable to IB (=Internal Breakdown) and GSD (=Green-Soft Disorder) which has to be considered seriously.   Regarding papaya, they are normally harvested green and after undergoing a fungal-dip cleaning process are packed carefully to prevent skin damage before been transported to the relevant markets via air under the local SCR incentive competitive freight rates.  Nevertheless, improved post-harvest storage and the lengthening of shelf-life would certainly facilitate sea-transport making it a very viable competitive marketable product.

At the import destination unpacking the fruits make them extremely vulnerable to ripening and hence shortening shelf-life.   Taking this aspect into consideration, the current study was undertaken to possibly isolate yeast and fungi from peel skin of the local lime, Citrus aurantifolia (CHRISTM) SWINGLE, from ten different localities in the Island  of  Penang (Figure 1) which could consequently be used as the organisms for such purposes.  Identification of these isolated microbes indicated the existence of Penicillium sp.¹, Penicillium sp.², Monilia sp., Trichoderma Koningi, Aspergillus niger, Aspergillus oryzae, Pichia sp. and Cephalosporium sp. at various intensities depending on the originating locality. (Figure 2)

The isolated and identified yeast and fungi were tested against controls for their effects on the ripening skin colour index of banana, Musa sapientum (Senorita), papaya, Papaya exotica, and star-fruit, Averrhao Carambola L., under exposure at varying concentrations of spores/cells/gms per ml.   With reference to Musa sapientum the controls void of any treatment attained a ripening skin colour index (Plate 1) of 6.8 after 4 1/2 days while the treated   lots at varying indexes after 6 days (Figures 3-10).  The lowest indexes after 6 days were shown by Penicillium sp.¹ at an exposure of 1 x 10⁴ spores/ml with a value of 2.8 followed by Cephalosporium sp. at 1 x 10⁴ cells/ml indicating a value of 3.9 and Monilia sp. at 1 x 10⁴ spores/ml having a value of 4.3.  The percentage of retardation in ripening skin colour index of the above mentioned yeast and fungal species were 58.82, 42.65 and 36.76, respectively, prolonging shelf-life considerably.

Similarly, in relation to Papaya exotica the control displayed a ripening skin colour index of 6.5 after 5 days while the best treatments of Penicillium. sp.² at 1 x 10⁶ spores/m1; 2.1, Penicillium sp.¹ at 1 x 10¹⁰ spores/ml; 2.4 and Aspergillus niger at 1 x 10⁶ spores/ml., 2.3, after incubation for 7 days.  These values transpire a percentage  retardation in ripening skin colour index against the control by 67.69, 66.15 and 64.61, respectively.  (Figures 11-18)

With regard to Averrhao carambola L. the ripening skin colour index for the control after 6 days was 5.6 while the best responding treatments of Penicillium sp.¹ at 1 x 10⁴ spores/ml; 3.7, Penicillium sp. at 1 x 10⁴, Trichoderma koningi at 1 x 10⁶ spores/ml and Pichia sp. at 1 x 10¹⁰ cells/ml; 4.0, (Figure 19-26).  The percentage of retardation in ripening skin colour index against the control are 30.36 for the Penicillium sp.¹ treatment while for the remaining aforementioned treatments as 28.57.

Based on the obtained results, it is apparent that biopreservation of local fruits, viz. Musa saapientum (Senorita), Papaya exotica and Averrhao carambola L., to prolong shelf-life is feasible by 2-4 weeks which is certainly very promising and could possibly be of much beneficial use within   the domestic and export ventures of perishable fruits.  For a vivid visualization of the biopreservation process the best results for all the three experimented fruits as compared to the controls are indicated in Plate 2 A, B & C.

References

Looney, N E. 1973.  Control of fruit maturation and ripening with growth regulators.  Acta Horticulturae, 34:397-406.

McGlasson, W B, Wade, M L and I Adato, 1978.   Phytohormones and fruit ripening.  In: Plant Hormones and Related Compounds - A Comprehensive Treatise.  Vol. 2. D S Letham, P B Goodwin and T J V Higgins.   Eds.  ASP Biological and Medical press.  B V Amsterdam.  39-128.

Wittwer, S H. 1971.  Growth regulators in agriculture.   Outlook Agric, 6:205-217.

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